Metalloid Ni2P and its behavior for boosting the photocatalytic hydrogen evolution of CaIn2S4

The development of high-efficiency and low-cost photocatalysts in photocatalytic H₂ evolution systems from water remains challenging. The substitution of a noble metal as the co-catalyst is still one of the important and meaningful issues in this field. Herein, we report a series of CaIn₂S₄ catalysts combined with Ni₂P, which acts as the co-catalyst, for boosting photocatalytic hydrogen evolution under visible light. The integrated system of the Ni₂P/CaIn₂S₄ composite exhibited high efficiency and durability, which were even higher than those of Pt decorated catalysts. The promoting effect of Ni₂P can be ascribed to its excellent reductive ability and analogous metallic character, which can accelerate the transfer and consumption of the photo-generated electrons. Moreover, based on the surface photo-voltage technique and electrochemical tests, the unique mechanism of Ni₂P for the movement of photo-generated charges during the photocatalysis process is proposed for the first time.     

Facile synthesis of carbon encapsulated RuO2 nanorods for supercapacitor and electrocatalytic hydrogen evolution reaction

In this work, carbon encapsulated RuO₂ nanorods (RuO₂ NRs/C) has been synthesized by thermolysis of ruthenium chloride and Punica granatum (P. granatum) peel under N₂ atmosphere. The synthesized RuO₂ NRs/C was characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction method (XRD), field emission scanning electron microscopy (FE-SEM) and high-resolution transmission electron microscopy (HR-TEM) with energy dispersive spectroscopy (EDS) analyses. The FT-IR results suggested that the organic constituents of P. granatum have been carbonized and encapsulated over RuO₂ nanorods (RuO₂ NRs). The XRD pattern of RuO₂ NRs/C revealed its crystalline nature and carbon encapsulation. The synthesized RuO₂ NRs/C has been well dispersed with the average width of 20 nm, exposed from the FE-SEM and HR-TEM images. The EDS results of RuO₂ NRs/C showed the existence of three elements viz., Ru, O and C. Further, the supercapacitor and electrocatalytic hydrogen evolution reaction (HER) activities of RuO₂ NRs/C were studied using standard electrochemical methods. The synthesized RuO₂ NRs/C offered a maximum specific capacitance of 151.3 F g⁻¹ at a scan rate of 5 mV s⁻¹, obtained from the cyclic voltammetry results. The onset over potential and Tafel slope of synthesized RuO₂ NRs/C for HER were −0.099 V_RHE and −99.4 mV dec⁻¹, respectively. The present study revealed that RuO₂ NRs/C as a better candidate for supercapacitor and HER.     

Walnut shell-derived hierarchical porous carbon with high performances for electrocatalytic hydrogen evolution and symmetry supercapacitors

Walnut Shell-derived hierarchical porous carbon has been successfully synthesized by the efficient KOH activation process. The hierarchical porous carbon material activated at 600 °C, has the specific micropore area of 1037.31 m² g⁻¹ and micropore volume of 0.51 cm³ g⁻¹, which leads to have electrochemical performances of the hydrogen evolution reaction (HER) and supercapacitors. Specifically, as the hydrogen evolution reaction electrocatalyst, the walnut shell-derived carbon material activated at 600 °C exhibits a lower onset potential of 6.00 mV, a smaller Tafel slope of 69.76 mV dec⁻¹ and outstanding stability above long-term cycling. As a supercapacitor electrode material, the sample possesses specific capacitance of 262.74 F g⁻¹ at 0.5 A g⁻¹, the remarkable rate capability of 224.60 F g⁻¹ at even 10 A g⁻¹ and good long-term stability. A symmetric supercapacitor shows the highly energy density of 7.97 Wh kg⁻¹ at a power density of 180.80 W kg⁻¹. This novel and low-cost biomass material is very promising for the electrocatalytic water splitting and supercapacitors.     

Nanoscale engineering MoP/Fe2P/RGO toward efficient electrocatalyst for hydrogen evolution reaction

The preparation of hydrogen evolution reaction (HER) electrocatalyst with high catalytic performance is a huge challenge. In this work, we develop a MoP/Fe₂P/RGO composite as a electrocatalyst for HER. The MoP/Fe₂P/RGO exhibits excellent electrocatalytic performance with a Tafel slope and an onset overpotential of 51 mV/dec and 105 mV, respectively. To drive 10 mA/cm², it only requires a small over-potential of 156 mV. The high electrocatalytic HER activity is mainly due to the synergistic effect of MoP and Fe₂P. In addition, the introduction of RGO not only prevents particle aggregation and coalescence during high temperature phosphating, but also improves the conductivity of the catalyst.     

Facile synthesis of NiS2 nanowires and its efficient electrocatalytic performance for hydrogen evolution reaction

Recently, the first-row transition metal dichalcogenides MX₂ (M = Fe, Co, Ni; X = S, Se) have been widely reported as promising catalysts for hydrogen evolution reaction (HER) because of its excellent catalytic activity and earth-abundance. The rational nanostructure designs have been proved as an effective way to improve their catalytic performance. However, the reported one dimension (1D) NiS₂ nanowires for HER suffer from a large Tafel slope. Here, we report a facile synthesis of 1D NiS₂ nanowires and its high efficient catalytic activity in HER. This nanowire structure with large surface area and active sites enables highly efficient electrocatalytic performance in HER with a much smaller Tafel slope (83.5 mV/dec) compared to that of bulk NiS₂ (136 mV/dec) as well as long-term stability. Our work builds up a structure–performance relationship and enriches the synthetic strategy to other efficient catalysts such as first-row transition metal dichalcogenides or transition metal phosphide.     

Plasmonic Au nanoparticle-decorated Bi2Se3 nanoflowers with outstanding electrocatalytic performance for hydrogen evolution

Hydrogen production from water splitting through electrocatalytic or photoelectrochemical route shows great potential for renewable energy conversion. Herein, the plasmon-enhanced photoelectrical nanocatalysts (NCs) have been successfully developed by Au nanoparticle-decorated Bi₂Se₃ nanoflowers (Au@Bi₂Se₃ NFs) as catalysts for hydrogen evolution reaction (HER), leading to a more than 3-fold increase of current under excitation of Au localized surface plasmon resonance (LSPR) and affording a markedly decreased overpotential of 375 mV at a current density of 10 mA cm⁻². The HER enhancement can be largely attributed to effective electron-charge separation and the increase of carrier density in Bi₂Se₃ induced by the injection of hot electrons of Au nanoparticles. Meanwhile, Bi₂Se₃ nanoflowers (NFs), a kind of topological insulators, possess gapless edges on boundary and show metallic character on surface, providing a path for the flow of electrons in the electrocatalytic system. This study opens up a new avenue towards the design of higher energy conversion catalytic water splitting systems with the assistance of light energy, which could increase of HER catalysis efficiency by plasmonic excitation.     

Polysulfide functionalized reduced graphene oxide for electrocatalytic hydrogen evolution reaction and supercapacitor applications

Functionalized carbon based 2D materials are promising candidates for low cost and environment friendly electrocatalyst for hydrogen evolution reaction (HER) and supercapacitor applications. To overcome the limitations posed by the noble metals and transition metal based composites, we have successfully synthesized metal free polysulfide functionalized reduced graphene oxide (GPS) in a simple chemical route. Structure and morphology of the material are characterized via XRD, FTIR, Raman, TEM, XPS measurements. The material behaves as an efficient HER electrocatalyst in acidic medium as well as energy storage device. It shows an onset potential of 97 mV and overpotential of 254 mV to reach a high current density of 10 mA/cm². DFT calculations are carried out to understand the structural stability and identification of active sites of the material. Boosting catalytic activity via increasing the number of active sites is an elegant approach. In this material we have used the S atoms of polysulfide polymer to facilitate hydrogen adsorption and desorption, thus improving the hydrogen evolution ability. The supecapacitor attains the high specific capacitance 347 F/g at the current density of 1 A/g. The origin of such performances is due to synergistic effect of both the graphene network and the polysulfide functionalizations.     

Flower-like CoS2/MoS2 nanocomposite with enhanced electrocatalytic activity for hydrogen evolution reaction

Molybdenum sulfide (MoS₂) has received tremendous attracts for its promising performance in the aspects of hydrogen evolution reaction (HER). To improve the HER activity of MoS₂, we designed a flower-shaped CoS₂/MoS₂ nanocomposite with enhanced HER electroactivity compared with MoS₂ nanosheets by a simple one-step hydrothermal method. The facile approach brings about distinct transformation of the morphology from nanosheets to nanoflower structures. The introduction of Co element into MoS₂ results in the larger active surface area, more edge-terminated structures, and higher conductivity of the CoS₂/MoS₂ nanocomposite, which are good for improving the HER electroactivity. In brief, the optimized catalyst exhibits the low overpotential of 154 mV at 10 mA cm^?2, small Tafel slope of 61 mV dec^?1, and excellent stability in acidic solution.     

Phase evolution and electrocatalytic performance for the hydrogen evolution reaction of MoxRe1-xS2 nanosheets

Transition metal doping is an effective method to induce a structural phase transition and improve the electrocatalytic performance of transition metal chalcogenides (TMDs). In this study, Mo_xRe_1-xS₂ nanosheets with Mo fraction x from 0 to 1 were grown on a carbon nanotube/carbon cloth (CNT@CC) substrate using a hydrothermal method by changing the molar ratio of Na₂MoO₄·2H₂O to NH₄ReO₄ in the precursor solution. The effect of the Mo fraction x on the phase structure and electrocatalytic performance for the hydrogen evolution reaction (HER) of Mo_xRe_1-xS₂ nanosheets was studied. The results indicated that Mo_xRe_1-xS₂ consists of the 1T′ phase (Re, Mo)S₂ and the 2H phase (Mo, Re)S₂, and the proportion of the 1T′ phase is in the range of 40–50%. Mo_0.5Re_0.5S₂/CNT@CC shows the best HER catalytic activity with an overpotential of 85 mV at a current density of 10 mAcm^?2, a Tafel slope of 38 mV dec^?1 and a charge transfer resistance of 1.04 Ω. This excellent HER catalytic activity is attributed to the phase transition, defects and S vacancies on the basal planes, as well as the synergistic effect between the Mo_xRe_1-xS₂ nanosheets and CNT.     

MoS2 confined on graphene by triethanolamine for enhancing electrocatalytic hydrogen evolution performance

The reduction of active sites due to reunion and slow electron transfer rates and low electronegativity greatly reduced the catalytic performance of many two-dimensional materials. In this paper, we synthesized composites for partially reducing graphene oxide and molybdenum disulfide (MoS₂@prGO) by one-step hydrothermal method. With the addition of triethanolamine, MoS₂ is highly dispersed on the prGO carrier and converted into the 1T phase MoS₂ (50.4%). Meanwhile, it helps to increase the electron transfer rate of the MoS₂@prGO composites. MoS₂@prGO composites presents a high electron cloud density due to the existence of N atoms and prGO, which promotes the occurrence of hydrogen ion conversion hydrogen reaction and decreases the electrocatalytic hydrogen evolution overpotential. MoS₂@prGO composites exhibits an overpotential of 263 mV at 10 mA/cm² and a small Tafel slope of 60 mV/dec. This work is devoted to offer a new prospect and direction for the improvement of electrochemical HER performance.     

Defect-rich MoS2 nanosheets vertically grown on graphene-protected Ni foams for high efficient electrocatalytic hydrogen evolution

Defect-rich MoS₂ nanosheets are vertically grown on graphene-protected Ni foam by a facial hydrothermal route. The vertically aligned MoS₂ nanosheets with defects such as cracks, amorphousness and oxygen-incorporated disorders endow these as-synthesized catalysts with rich active sites, high conductivity and good stability. The graphene deposited on Ni foam increases its stability in acid. The optimized catalyst exhibits high activity for hydrogen evolution with a quite low overpotential of 140 mV at 10 mA cm^?2, a small Tafel slope of 42 mV decade^?1, and a large exchange current density of 63 μA/cm², as well as excellent stability. This performance is superior to most of its analogue MoS₂ and many transition metal sulfides. This work will broaden the vision to improve the activity of self-supported electrocatalysts by carefully designing the anchored catalysts.     

Rod-like nonstoichiometric Ni0.85Se as efficient electrocatalysts for hydrogen evolution reaction

Nickel selenides with different Ni/Se atomic ratio have been successfully synthesized by a simple solvothermal method. Among them, the nonstoichiometric compound (Ni_0.85Se) (A-10) behaved excellent electrochemical catalytic activity towards hydrogen evolution reaction. Furthermore, it presents an ultra-low overpotential (η) of 190 mV and extremely small Tafel slope of 57 mV/dec when the current density j_A reaches ～10 mA/cm². At the same time, it has large effective electrochemical active surface area and shows outstanding stability after a long time chronoamperometry testing.     

Electrochemical performance of porous Ni3Al electrodes for hydrogen evolution reaction

Porous Ni₃Al intermetallic material with a mean pore diameter of around 1 μm was prepared by step sintering Ni and Al powder pressed compacts in vacuum furnace at 900 °C. The electrocatalytic activity of the as-fabricated porous Ni₃Al material as an electrode for hydrogen evolution reaction (HER) in alkaline solutions was investigated by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. It is found that the onset potential of porous Ni₃Al for HER shifted in the positive direction favoring hydrogen generation with lower overpotential, compared with foam Ni and dense Ni electrodes. Effects of electrolyte concentration and temperature on HER as well as the electrochemical stability in alkaline solution were investigated and the electrochemical activation energy was determined for the porous Ni₃Al. The increased activity for HER was attributed to the high porosity, an increased electrochemical surface area and the nanostructure of porous Ni₃Al electrode. The corrosion tests showed that the corrosion resistance of porous Ni₃Al electrode changed during the immersion process due to the formation of passive film layers.     

Facile synthesis of MoS2/CuS nanoflakes as high performance electrocatalysts for hydrogen evolution reaction

The fabrication of metal sulfides heterostructure is a promising strategy for enhancing catalytic activity. Herein, the MoS₂/CuS heterostructure was successfully grown on carbon cloth (MoS₂/CuS/CC) through an efficient method. The SEM results confirmed that the fabricated MoS₂/CuS/CC composites have a flake morphology, which can not only improves the surface area but also offers ample surface catalytic active sites. Particularly, the optimized MoS₂/CuS/CC-2 electrocatalyst showed a small overpotential of 85 mV@10 mA cm^?2 and exceptional long-term cycling durability for hydrogen evolution in 1 M KOH. The outstanding catalytic activity is attributed to the fact that the combination of MoS₂ with CuS can greatly enhance the charge transport rate and improve the structural stability. These results suggest that the MoS₂/CuS/CC heterostructure is a potential electrocatalyst for hydrogen production.     

Nanostructure and stoichiometry tailoring of CoS2 for high performance hydrogen evolution reaction

Developing efficient and low-cost electrocatalysts for hydrogen evolution reaction (HER) is important for hydrogen fuel production. In this study, we synthesized two different types of CoS₂ under low sulfur (LS) and high sulfur concentration (HS) conditions. Structural analysis results show that CoS impurity phase forms easily when the concentration of sulfur is low, while at high sulfur concentration the growth of CoS impurity phase is inhibited and leads to phase-pure CoS₂. Electrochemical investigation of HER performance reveals that the onset potential of CoS₂ (HS) electrode (ca. − 0.11 V vs. the reversible hydrogen electrode, RHE) is 30 mV anodic of the CoS₂ (LS) one (ca. − 0.14 V vs. RHE). At a specific current density of 10 mA cm⁻² the required overpotential on CoS₂ (HS) electrode is only 163 mV, which is 40 mV less than the CoS₂ (LS) electrode. Electrochemical impedance spectroscopy (EIS) data further demonstrate that the charge transfer rate of CoS₂ (HS) electrode is faster than that of CoS₂ (LS) electrode towards HER.     

Large surface and pore structure of mesoporous WS2 and RGO nanosheets with small amount of Pt as a highly efficient electrocatalyst for hydrogen evolution

In this work, mesoporous WS₂ with high surface area was prepared by hard template method. First, a one-step nanocasting generates metal precursor@mesoporous silica SBA-15 composites. A hydrothermal method is subsequently adopted to convert the precursors to sulfides in the confined nanochannels. After etching silica SBA-15, mesoporous layered metal sulfide crystals were obtained as the products. Then, we have put forward a new catalyst based on mesoporous WS_2, RGO nanosheets and Pt nanoparticles as a highly efficient electrocatalyst for hydrogen evolution. The Pt/WG-2 nanostructure electrocatalyst in this report exhibits excellent performance with a small Tafel slope of 47 mV dec^?1, long-term durability and an overpotential of 95 mV in 0.5 M H₂SO₄ for the hydrogen evolution reaction (HER).     

Hierarchical MoS2 nanosheets integrated Ti3C2 MXenes for electrocatalytic hydrogen evolution

In this study, conductive Ti₃C₂ MXenes were used as a promoter to accelerate charger transfer of MoS₂, realizing highly efficient HER electrocatalysis. A facile hydrothermal strategy is demonstrated to be effective for in situ growth of MoS₂ nanosheets vertically standing on planar Ti₃C₂ nanosheets to form hierarchical heterostructures. Beneficial from the opened layer structures and strong interfacial coupling effect, the resulting MoS₂/Ti₃C₂ heterostructures achieve a giant enhancement in HER activity compared with pristine MoS₂ nanosheets. More specifically, the catalytic current density induced by MoS₂/Ti₃C₂ heterostructures at an overpotential of ∼400 mV is nearly 6.2 times as high as that of the pristine MoS₂ nanosheets. This work uncovers that the Ti₃C₂ nanosheets are ideal candidates for construction of highly active electrocatalysts for water splitting.     

Ultrathin molybdenum disulfide nanosheet-coated acetylene black: One-pot synthesis and electrocatalytic hydrogen evolution

Molybdenum disulfide (MoS₂) and its composites are the promising electrocatalysts for the hydrogen evolution reaction (HER) in acidic solution because it is earth-abundant and low-cost. Here we reported the ultrathin molybdenum disulfide nanosheet-coated acetylene black (AB) coated (MoS₂@AB) as the electrocatalysts for the HER. The catalysts were synthesized in a facile one-pot solvothermal route. The as-prepared catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution TEM, X-Ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). The results show that the MoS₂ nanosheets on AB have a few layers and many surface defects, which are benefical to the HER catalysis. Electrochemical tests revealed that the existence of AB can't only make the catalyst expose a considerable amount of active sites but also increase the turnover frequency (TOF) value per site. In addition, the MoS₂@AB(75) had excellent electro-catalytic HER performances with a low onset potential (−110 mV), a small Tafel slope (50–60 mV per decade) and the longtime stability (10 h).     

Synthesis of nitrogen-doped MoSe2 nanosheets with enhanced electrocatalytic activity for hydrogen evolution reaction

Benefiting from improved electrical conductivity, the N-doped MoSe₂ nanosheets show substantially enhanced HER activity with a lower onset overpotential of approximately ?135 mV and a smaller Tafel slope of 62 mV dec^?1, which exhibiting enhanced catalytic performance compared with that of pure MoSe₂. The success of improving the HER performance via the introduction of N dopant offers a new opportunity in the development of high performance MoSe₂-based electrocatalyst.     

Rational design of PANI incorporated PEG capped CuO/TiO2 for electrocatalytic hydrogen evolution and supercapattery applications

Synthesis of efficient electrocatalysts for energy applications is a major area scientists are currently focusing on to address the twin challenges of energy shortfall and the production of clean energy. Herein, an efficient electrocatalyst, polyaniline incorporated with polyethylene glycol capped CuO/TiO₂ is prepared, which is effective in hydrogen evolution reactions and energy storage applications. The characterizations like XPS, XRD, FT-IR, FE-SEM, HR-TEM, and BET have been carried out to confirm the successful formation of the synthesized PANI/CuO/TiO₂ composite. At 10 mA/cm² current density, the prepared composite exhibits a lesser overpotential of 536 mV and 1587.2 C/g at 1 A/g as the specific capacity. The electrode prepared using the PANI/CuO/TiO₂ composite also shows cyclic stability up to 2000 cycles. The synthesized composite is an efficient electrocatalyst for energy related applications.